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Self-descriptive Numbers & List Methods

Posted in Education, and WhoCodeFirst


Write a script to display the first three self-descriptive numbers.


say '1210, 2020, 21200'. On to the next task. Not so quickly  🙂 While the above would produce the expected output, that’s not the spirit of what the weekly challenge is about.

For this task I ran an incrementing loop that exited once three self-descriptive numbers were found. The main part of the logic appears in the _is_self_descriptive subroutine. I first convert the number into an array of occurrences. For example 12140 would be turned into 1,2,1,0,1,0,0,0,0,0. I then compare this with the digit in the position, and return false undef or true 1 if there is a match.


» ./ 
1210, 2020, 21200


Write a script to list methods of a package/class.


For caveats first.

  • In the real world, I would simply use Class::Inspector‘s methods function. There is no need to re-invent a perfectly working wheel.
  • My solution won’t list inherited methods. We could walk the @ISA tree, but this seems more complicated than required for the task.
  • Likewise it won’t show autoloaded methods.
  • My code is loosely based on Class::Inspector

And with all of that, there isn’t much else to say. I require the package, and then look up everything in its table, and exclude everything that it’s a sub-routine (e.g variables).

If a package is not supplied, then Calc is assumed.


» perl -I . ./ 
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